1. Field of the Invention
The application is a 371 of PCT/EP99/09145 filed Nov. 25, 1999, now WO 00/31029.
The present invention relates to a process for the preparation of organic disulfides.
Various processes for the preparation of organic disulfides are known from the prior art.
2. Description of the Background
EP-A 0 171 092 describes a process for the preparation of dialkyl disulfides in which alcohol, sulfur and hydrogen sulfide are reacted directly to give dialkyl disulfides and water. The process is preferably carried out over a zeolite-based catalyst, at temperatures of from 200 to 400xc2x0 C. and in a pressure range from atmospheric pressure to 600 psig. A disadvantage of this process is that multicomponent product mixtures are obtained from which the dialkyl disulfide can only be isolated in poor yields (approximately 50% of the theoretical yield).
U.S. Pat. No. 5,202,494 describes a process in which mercaptan is reacted with oxygen over an MgO/Na2O-doped aluminum oxide catalyst to give dialkyl disulfide and water. The process produces high-boiling components, which have to be removed from the system during distillative work-up.
FR-B 1 358 398 discloses a process for the preparation of dialkyl disulfides from mercaptans and elemental sulfur in which the sulfur is used in the form of a solution in an organic solvent, in particular in an organic dialkyl disulfide. The catalysts used are amines. A disadvantage of this process is that clean, and therefore expensive, mercaptans have to be used as starting materials.
It is therefore an object of the present invention to provide a process for the preparation of organic disulfides which starts from low cost and readily available raw materials and provides the desired dialkyl disulfide in good yields.
We have found that this object is achieved by a process for the preparation of organic disulfides by oxidation of mercaptans with sulfur dissolved in an organic disulfide using an amine as catalyst. The process according to the invention comprises using the mercaptans as xe2x80x9ccrude mercaptan streamxe2x80x9d from a reaction of alcohols with hydrogen sulfide over a catalyst suitable for mercaptan synthesis.